With cases reported in a number of countries, human monkeypox infection is generating global interest and concern as an emerging infectious disease threat even in the midst of a slowly relenting COVID-19 pandemic.
What is monkeypox virus?
Monkeypox is a member of a closely related group of viruses in the Orthopoxvirus genus that includes smallpox, cowpox and camelpox. Monkeypox virus was first discovered in the summer of 1958 as a non-lethal, smallpox-like, skin disease of captive monkeys at a research institute in Denmark.
Transmission occurs through close physical contact with animals or humans, their body fluids, contaminated droplet particles from respiratory secretions or infected skin lesions and indirectly by way of “fomites” (inanimate objects such as bed linens, towels and hard surfaces that may be laden with infectious virus particles).
When was monkeypox first reported in non-African countries?
The first cluster of human monkeypox infections outside of Africa occurred in the United States in 2003. A multi-state outbreak involving 87 children and young adults was attributed to close contact with infected prairie dogs acquired as pets from an animal distributor. The ultimate source of infection was found to be imported Gambian rats that transmitted the infection to the prairie dogs. There were no human deaths, although three children experienced severe illness.
The incubation period of monkeypox in humans ranges from four to 21 days and is followed by a one- to five-day phase of fevers, chills, sweats, fatigue and enlarged, tender lymph nodes in the neck and groin.
The next phase involves a multi-stage rash that progresses from small skin patches to papules (small bumps on the skin), followed by vesicles (small bumps filled with clear fluid) and then pustules (small bumps filled with pus). These are most prominent on the face, palms and soles of the feet. The pustules resolve by scarring or crusting over in the ensuing two to four weeks.
Exposed people may also develop a sore throat, cough and/or a rash on the mucous membranes of the mouth.
How severe is monkeypox infection?
The disease is usually mild, although severe illness and death can occur. There are two common genetic variants of monkeypox virus: the Central African variant and the West African variant. Mortality rates of 3.6 per cent for the West African variant and 10.6 per cent for the Central African variant have been reported in endemic regions.
Are there any other public health recommendations for monkeypox?
People who are infected with monkeypox should wear surgical masks, and skin lesions should be covered until they have healed. Personal use items such as towels and sheets should not be shared. Frequently touched surfaces should be regularly disinfected, contaminated clothing should be laundered and contact with household and non-household members should be avoided until the illness has resolved.
Health-care workers should use gloves, gowns and respiratory protection with N95 masks and face shields, and maintain excellent hand hygiene while caring for patients with monkeypox. Hospitalized patients with confirmed or suspected monkeypox should be isolated with precautions for airborne, droplet and contact transmission until they are no longer contagious.
The U.S. Centers for Disease Control and Prevention’s Advisory Committee on Immunization Practices recommends pre-exposure prophylaxis (vaccination prior to exposure to the virus) with the newer generation vaccine for laboratory workers performing monkeypox diagnostic testing, as well as for health-care workers administering smallpox vaccine or caring for patients with monkeypox. (Its trade name is Jynneos in the U.S., Imvamune in Canada and Imvanex in Europe.)
In Canada and other developed countries, people born before 1972 were likely vaccinated against smallpox. Although immunity following vaccination tends to wane with age, lifelong immunity appears to be the norm following smallpox vaccination in otherwise healthy individuals, and its cross-protective efficacy against monkeypox is believed to be 85 per cent.
Is monkeypox the next viral pandemic?
The emergence of infectious diseases such as monkeypox in non-endemic areas has created a great deal of anxiety in light of our experience with COVID-19.
Monkeypox had been a neglected tropical disease until the current outbreak in the developed world. But the trajectory of these cases, coupled with the pattern of transmission in Africa, suggests that the virus will not become pandemic.
The basic reproduction number (R0), a measure of viral contagiousness, where R0 equals the number of secondary infections transmitted from a single case in a non-immune population, is 0.6 to 1.0 for the Central African variant, and much lower for the West African variant.